The Fundamental Controls of Compressors

The best professional mixing engineers are typically also the best professional lazy people. Instead of having to manually ride faders constantly engineers decades ago invented an automatic volume automation tool and called it a compressor.

In this tutorial, Fab Dupont explains the most essential controls on this powerful and often confusing studio staple.

Fab explains what each knob does and gives you easy-to-remember tips that will simplify the process of dialing in your own compressor settings.

Compressor controls covered:

Threshold

Ratio

Make-up gain

Attack

Release

Learn how to set your compressor to gently kiss the peaks or rudely slap around the input signal with Fab's detailed explanations and clear audio examples.

Compression has a signature sound to it - once you hear it and understand exactly what's going on you can truly be in control over the tone, level and speed of your tracks.

00:02:04As you can see on the waveform,
the "Plak! Plak!" is much louder
than the "Tchugga, Tchugga".

00:02:09Let's say I want to take care
of the "Plak! Plak!"
but not the "Tchugga, Tchugga."
I'm gonna lower my threshold
so that the bar hits the "Plaks",
but not the "Tchugga, Tchugga!"
And it sounds like this.

00:02:30Now, every time the "Plak!" happens,
because of where I put my threshold,
some gain reduction's happening.
The difference in sound is staggering.

00:02:37This is flat...

00:02:43And this is with the compression.

00:02:49Again, without...

00:02:56With...

00:03:03Only the loud part of the signals
are compressed.

00:03:06If I want to be a hooligan
and go lower,
all I have to do is lower the threshold
and everything is gonna get compressed,
and it sounds like this...

00:03:23Definitely for hooligans.
So let's bring it back up
to something slightly more reasonable.
Ever so slightly more reasonable...

00:03:33Fair enough!
So now we know which part of the signal
we want to compress
using the threshold control.

00:03:39The next question is
how much do you want to compress it,
and that's the job
for the ratio control.

00:03:44The ratio control determines
the amount of gain reduction.

00:03:47Meaning, it controls how far down
your automated fader is gonna go.

00:03:51This involves some maths, which will
bring you back to your High school days
only without the sweetheart,
or the popularity contents.

00:03:58It's a division, it's a ratio.

00:03:59So for example,
if you have a 2:1 ratio,
it means that any signal
over the threshold
will get divided by 2 level-wise.

00:07:25If you're compressing something a lot,
it's gonna bring the level down a lot,
like we saw.

00:07:30For you to be able to compare
original and compressed signals,
you need gain to bring the compressed
signal back up to the original level,
so you can truly compare the difference
in tone, and not just in level.

00:07:40That's what the gain button is for.

00:07:43In the case of the cajón,
it would do something like this.

00:07:46This is my raw signal.

00:07:49The compressed signal...

00:08:06So now, I can really tell
what I'm doing to my signal,
I'm being rude!
Which brings me to my next point!
Here's what's going on.

00:08:13My compressor is bringing
the high level down.

00:08:17And then the gain is bringing
the whole thing up.

00:08:20As a result, the low levels, which
were low, are now being brought up.

00:09:00So I'm bringing all the bleed
from the other instruments up,
so it's being compacted, or compressed.

00:09:05Now, that's a good thing,
you can make cool sounds.

00:09:08But say you have
a snare drum that's recorded
that has quite a bit of hi-hat in it.
What's gonna happen?
The difference between the snare
and the hi-hat is gonna go "Pfff..."
and you're gonna have as much
hi-hat as snare in your snare mic.

00:09:19You know how that feels.
That gives you a nose bleed.

00:09:22That sucks. You don't want to go there.

00:09:24You have to be careful what you do with
your compressor and your make-up gain.

00:09:27That's the art of it.

00:09:29One last consideration for
the gain button is that of gain staging.

00:09:32It is great to strive and keep levels
consistent pre and post compression,
pre and post any processing, really.
It's great for comparison,
but it is also great to hit
your hardware, your plug-ins,
your converters in their sweet spot,
just like you saw in
the Recording Level video, did you not?
So we have threshold, we have ratio,
we have gain, we're gonna
move on to attack and release.

00:09:56Or should I say
the almighty attack and release...

00:10:00Attack and release,
sometimes labeled time constants,
are the two settings that I see
confuse people the most.

00:10:06Probably in part because most
compressors are grossly mislabeled.

00:10:09They label everything as time,
where it should be labeled as speed.

00:10:12No, really, trust me!
That's the way it is.

00:10:15That's a speed control.

00:10:16What they mean is
dB per second settings.

00:10:20But we don't want to go there, because
that brings us back to High school
and all we want is a hit on the radio.
Let me show you how it really works.

00:10:27You could think of it this way.
There are two parties involved:
your brain, which listens to
the original signal, the music,
and decides how much
gain reduction it wants,
and your finger, that's supposed to
achieve that gain reduction on the fader.

00:11:03The beauty of this is you could have
coffee on the way down
and hangover on the way up,
or hangover on the way down,
and coffee on the way up,
meaning fast attack, slow release,
or slow attack, fast release.

00:11:15Wouldn't it be wonderful
to have that in real life?
Now let's look at practical examples.

00:11:20Let's focus on the attack control.

00:11:22Here's a standard snare,
with no compression.

00:11:31I'm gonna turn on the compressor.
My threshold is at -24 dB...

00:11:35with a ratio of 3:1.

00:11:37I'm opening the attack
all the way up, 300 ms.

00:11:39This is what it sounds like...

00:11:46Now the threshold is really low
and the ratio is appropriate,
why is nothing happening?
Well... this is what's happening.

00:11:53Since the attack is so slow,
the compressor is not fast enough
to reach for the fader in time
and bring it down, so basically,
this is what's happening.

00:12:02Oh! Sorry!
Oh! Sorry.

00:12:04Oh!
My bad...

00:12:07Let's do it again!
I'm too slow!
Now as you speed up the attack,
stuff happens. Check it out!
What's happening is that,
as I'm speeding up the attack,
my finger is getting faster and faster
at following the gain reduction orders
form my brain.

00:12:41As you speed up the attack further,
you get into transient control.

00:12:44Let me show you.

00:12:46Here's the same snare. I'm gonna start
with an attack of 4.2 ms,
which means absolutely nothing!
Let's call it "Speed 4.2",
and then I'm gonna speed it up.

00:13:08The transient gets nuked.
My finger is now fast
that it can grab the fader
and bring it down instantly,
killing the top of the snare sound,
taking all the punch away.

00:13:17Is that a good thing, or a bad thing?
That's a different discussion!
Let's talk about release.

00:13:22The release phase of a compression
cycle happens when your brain
tells your finger
to not compress as much.

00:13:27Why would your brain do that?
While your brain is listening to
the input signal,
if the input signal is not as loud,
you don't need to compress as much,
and it tells your finger:
"Yo! That's too much! Go back up."
The release control says
how fast that should happen.

00:13:42Here's our snare.
As you can see in the waveform,
we have a sharp transient,
a loud transient.

00:13:47And then we have a quieter tail.

00:13:50In this case,
I'm using a fast attack and release.

00:13:54What this is gonna do is that
the transient and the body of the snare
are gonna be at the same level.
And it sounds like this.

00:14:04On a snare
that really sounded like this.

00:14:09Again, with.

00:14:14That's a fast attack and release.

00:14:16That means that now, my transient
and my tail are at the same level,
and give this sound.
What happens if I lengthen the release?
This is what happens...

00:14:31As a reminder, the snare sounds
like this uncompressed.

00:14:38With the compression...

00:14:44What happens is this: the first snare
hits, and the attack is so fast
that the gain reduction fader
goes down here.

00:14:49But then the release is so slow,
that the gain reduction fader does not
have time to go back up
before the next snare hits
and tells it to stay there.

00:14:58It's actually going back up,
but so slowly that you can't hear it.

00:15:01Now why does it sound the same?
It sounds the same because...
Imagine this...

00:15:06Say this is my gain reduction fader,
and this is my Master.

00:15:10The red is the gain reduction,
the green is the Master.

00:15:13What is the difference between having
no gain reduction
and the Master down here,
or full gain reduction,
and the Master up here?
Zilch!
Side note number 1.

00:15:24When a compressor manufacturer
sells us on the fact
that his box can do 25 dBs
of totally transparent compression,
it means again: zilch!
The question is:
does it do it in static compression,
or can it do it in dynamic compression,
meaning the fader is moving?
If it's only static compression,
we might as well use a fader.

00:15:43Side note number 2.

00:15:45Why don't we use really fast
attack and release times
and enjoy a perfect link between
our brains and our gain reduction faders?
Because there are
problems associated with that.

00:15:54We just saw the transient problem,
here's another one.

00:15:58Some instruments like bass drums
and basses with long wavelengths
can distort really quickly
with fast attack and release times.

00:16:05The reason for this,
and I'm gonna simplify drastically,
is that the compressor gets confused
and reads the oscillation
of the waveform as volume changes
and tries to ride the waveform itself.

00:16:16In English, it don't sound so good.
Let me show you.

00:16:19Here's a bass recording.

00:16:26It sounds good.
Now I'm gonna quicken the attack.

00:16:37Distortion comes in.

00:16:39If I return the attack where it was
and quicken the release, this happens.

00:16:50With the two of them,
it sounds like this.

00:16:58If you're in this situation,
all you have to do is slow down
the attack, or the release, or both.
Season to taste.

00:17:05Side note number 3.

00:17:09A lot of people think that
attack and release phases
happen only when the signal
crosses the threshold.

00:17:16On the way up for attack,
and down for release.

00:17:19That ain't true!
It is true that the first attack phase
happens the first time
that the signal goes
above the threshold.

00:17:25But after that, it's independent.
Let me show you.

00:17:29This is what happens.

00:17:30As long as I'm above the threshold,
I'm compressing.

00:17:33Meaning my gain reduction fader
has movement.

00:17:36My brain still monitors
the source signal.

00:17:38If there are differences in level
in the source signal,
then my brain is gonna tell
my finger to react.

00:17:44If it gets louder, it's gonna say:
compress more.

00:17:46If it gets softer, it's gonna say:
compress less.

00:17:49The reality is that when I compress
more, there's an attack phase,
and if I compress less,
there's a release phase.

00:17:55Of course, none of that happens
in static compression,
but we don't do static compression,
we use faders.

00:18:00Chew on that!
In summary, we've looked
at five parameters.

00:18:04Threshold lets you decide which
part of the signal you want to process.

00:18:09Ratio lets you decide
how much you want to process
that part of the signal
you just singled out.

00:18:14Make-up gain lets you compensate
for the loss in volume
from heavy compression.

00:18:19Attack and release are gonna decide
how fast or how slow
you're gonna respond
to the changes in gain reduction.

00:18:25Understanding and mastering
those five parameters
will let you get away with murder.

00:18:30And I can hear you think from here,
there are other parameters
like Soft knee,
Peak or RMS detection,
Automatic attack and release,
Hold, Automatic gain...
We know that!
We will cover those other parameters
in a different video.

00:18:43Until then, go squish something!
Et voilà!

Once logged in, you will be able to read all the transcripts jump around in the video.

Fab Dupont is a Grammy winning NYC based record producer, mixing/mastering engineer and co-founder of pureMix.net.

Fab has been playing, writing, producing and mixing music both live and in studios all over the world. He's worked in cities like Paris, Boston, Brussels, Stockholm, London and New York just to name a few.

He has his own studio called FLUX Studios in the East Village of New York City.

Fab has been nominated for Grammys 6 times, including two Latin Grammys and has received many other accolades around the world, including Victoires de la Musique, South African Music awards, Pan African Music Awards and US independent music awards.

Fantastic video Fab. Even for those who have been using compressors for a while, it's great to back up for a moment and really get an understanding of what is going on...and you have done a marvelous job once again laying things out in a way that provokes methodical thought. Thank you. I've truly deepened by knowledge and changed the way I approach compressors.

GuitarLegend

2014 Dec 06

I don't mind spending money on an educational video that confirms what I already know but I thought this one was so basic that it could have been a freebie...

eike_ebbel

2014 Dec 04

I would love watching a video about 2-bus-compression. I know how
to handle comp settings on individual tracks but the last comp in chain makes
me struggle sometimes especially when it comes to finding the right attack and release
settings. Would be cool watching Fab do this special task in a special video.